The present invention relates to a method for producing fluoronitrobenzene compounds. Fluoronitrobenzene compounds such as 2-fluoronitrobenzene, 4-fluoronitrobenzene, and 2,4-difluoronitrobenzene, are useful as intermediates for the synthesis of various hebicidal compounds, dyes, and the like. Such compounds have been prepared from corresponding chloronitrobenzene compounds by so-called halogen exchange reactions, illustrated as follows: ##STR1## wherein MF represents an alkali metal fluoride salt. The reaction is generally conducted in an aprotic, polar, organic solvent, such as dimethylsulfoxide, dimethylformamide, tetramethylenesulfone, and the like.
Alkali metal fluoride salts are not soluble in such solvents, therefore, the reaction mixtures usually contain two phases, i.e., solid and liquid phases or two immiscible liquid phases. Finger, G. C., et al., J. Am. Chem. Soc., 78, 6034 (1956) and Duesel, B. F., et al., U.S. Pat. No. 3,064,058 (Nov. 13, 1962), describe the reaction of chloronitrobenzene compounds with finely-divided, solid potassium fluoride in aprotic polar solvents to produce corresponding fluoronitrobenzene compounds. Boudakian, M. M., et al., U.S. Pat. No. 3,240,824 (Mar. 15, 1966), describe the reaction of o-chloronitrobenzene with solid potassium fluoride at elevated temperatures, without any solvent or diluents, to produce o-fluoronitrobenzene. Napier, D. R., et al., U.S. Pat. No. 3,992,432 (Nov. 16, 1976), describe a reaction involving two liquid phases. In that method, the inorganic fluoride salt is dissolved in an aqueous phase, and the chloronitrobenzene compound is dissolved in a water-immiscible, organic phase. The reaction is catalyzed by a quaternary salt, which reportedly transfers ions across the phase interface.
Quaternary salt phase-transfer catalysts have also been used in solid-liquid, two phase reactions. For instance, Kunz, R. A., U.S. Pat. No. 4,069,262 (Jan. 17, 1978), describes the production of 2-fluoronitrobenzene by reacting 2-chloronitrobenzene with finely-divided potassium fluoride in tetramethylenesulfone solvent using a macrocyclic ether (crown ether) or a quaternary ammonium halide catalyst, and Tull, R. J., et al., U.S. Pat. No. 4,140,719 (Feb. 20, 1979), describes the production of 5-chloro-2,4-difluoronitrobenzene by reaction 2,4,5-trichloronitrobenzene with solid potassium fluoride in an anhydrous organic solvent in the presence of a quaternary ammonium halide catalyst.